There is a great emphasis on high productivity in the photosensitive materials market. Photofinishers that use photosensitive paper to produce color prints desire short processing times in order to increase output. One way to obtain rapid processing is to accelerate the development time by increasing the chloride content of the emulsions; the higher the chloride content the higher the development rate. However, it is also known that the higher the chloride content is, the harder it is obtain high, invariant photosensitivity. Emulsions that are primarily silver chloride are more difficult to spectrally sensitize than emulsions used previously such as silver bromide or chlorobromide emulsions because the conduction band of silver chloride is higher than that of silver bromide (C. R. Berry, Photo. Sci. & Eng. 19, 93, (1975)).
The problem with sensitizing efficiency is especially true in the red-sensitive layer of many color print photosensitive materials and is related to the red sensitizers reduction potential. Correlations between dye reduction potentials and sensitizing efficiency on high silver chloride emulsions are discussed by W. Vanassche, J. Photo. Sci., 21, 180 (1973) and P. B. Gilman, Jr., Photo. Sci. & Eng. 18, 475 (1974). Another common problem with the red sensitive layer of color print paper which contains an emulsion that is primarily silver chloride, is an undesirable sensitivity to temperature. An increase in temperature of the paper during exposure results in an increase in red speed of the red sensitive layer making it difficult for the photofinisher to adjust his printing conditions. This results in a loss in operating efficiency.
Among the red sensitizing dye structures reported that have been used in the red sensitive layer of color print paper are dicarbocyanines having a neopentylene bridge in the pentamethine chain, such as Comparison Dye C-1 (see Table IIA below) and similar dyes (Table IIA below). U.S. Pat. No. 2,875,058 indicates that it is often advantageous to use those dyes in combination with a nitrogen heterocycle such as a triazinylstilbene. Japanese Kokai 60-220,339 teaches the use of some of those dye types on silver halide emulsions that are 25% or more silver chloride. Dicarbocyanine dyes having a gem-dimethyl substituted neopentylene bridge have been reported in EP 0 313 021 and allegedly give improved thermal sensitivity when used with high chloride emulsions. Similar dyes are described in EP 0 313 022, EP 0 317 825, U.S. Pat. No. 4,618,570, EP 0 244 184, EP 0 368 356, EP 0 367 227, and EP 0 364 990.
It is desirable to provide photographic materials with a high silver chloride red sensitive layer which has a high sensitivity and exhibits reduced thermal sensitivity.